is there a way I could add a item from my inventory into deluxe menu shops?

[digital musk]

Is there any way I could add an item from my inventory to the deluxe menus shop? (it's sorta a custom item so it's very specific, and there's no command to give it to myself)

[rapid trellis]

The best way I can think to get your item information would be:
holding it and typing /data get entity @s SelectedItem

you can type /data get entity <user> SelectedItem to do it from console

it will return the raw json format of the item info